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@wikipedia 

Motivation


In some specific subsurface applications which require the knowledge of subsurface temperature distributions the assumptions of constant areal geothermal profile are assumption of the Constant Areal Geothermal Temperature Profile is not valid and the problem requires a proper 3D modelling solution.


Outputs

LaTeX Math Inline
body--uriencoded--T_G(t, %7B\bf r%7D)

LaTeX Math Inline
body--uriencoded--G_T(%7B\bf r%7D)

Geothermal Temperature Gradient


Inputs

LaTeX Math Inline
bodyt

Local Calendar Time

LaTeX Math Inline
body--uriencoded-- %7B\bf r%7D

Position vector

LaTeX Math Inline
bodyz(l)

LaTeX Math Inline
body--uriencoded--%7B\bf j%7D(

%7B\bf r%7D

x,y, z = z_%7Bref%7D)

Earth's Heat Flux at some reference depth 

LaTeX Math Inline
body--uriencoded--z = z_%7Bref%7D
 as function of 
LaTeX Math Inline
body (x, \, y)

LaTeX Math Inline
body--uriencoded--q(%7B\bf r%7D)

Volumetric density of heat sources distributed throughout the subsurface rock volume

LaTeX Math Inline
bodyT_s(t, x, y)

Surface temperature based on weather reports

LaTeX Math Inline
body--uriencoded--\lambda_e(%7B\bf r%7D)

Subsurface Thermal Conductivity profile as function of position vector

LaTeX Math Inline
body--uriencoded--a_%7Be%7D(%7B\bf r%7D)

Subsurface Thermal diffusivity profile as function of position vector

where

LaTeX Math Inline
bodyl

Measured Depth of wellbore trajectory with reference to Earth's surface (

LaTeX Math Inline
bodyl=0
)

LaTeX Math Inline
bodyz_s = z(l=0)

TVDss of the Earth's surface in a given location. In case the Earth's surface is at sea level then 

LaTeX Math Inline
bodyz_s = 0


Assumptions




Equations


LaTeX Math Block
anchorT_z
alignmentleft
T_G(t, {\bf r}) = T_{GS}({\bf r})  + T_Y(t, z) + T_D(t, z)
LaTeX Math Block
anchorG_T
alignmentleft
G_T({\bf r}) = \frac{j_z}{\lambda_r({\bf r})}
LaTeX Math Block
anchor1
alignmentleft
\nabla T_{GS} = \lambda^{-1}
\rho_e \, c_e \frac{\partial T_G}{\partial t} + \nabla \left( \lambda_e \nabla T_G \right) = q({\bf r})
\cdot {\bf j} LaTeX Math Block
anchorrot_j
alignmentleft
\nabla \times {\bf j} = 0



LaTeX Math Block
anchor1
alignmentleft
 T_
{GS}(
G(t, x, y, z = z_s) = T_s
LaTeX Math Block
anchorT_z
alignmentleft
T_Y
(t,
z) = \delta T_A \, \exp \left[ \, {(z_s-z}) \sqrt{\frac{\pi}{a_{en} \, A_T}} \, \right] \, \cos \left[ \, 2 \pi \frac{t - \delta t_A}{A_T} + (z_s -z) \sqrt {\frac{\pi}{a_{en} \, A_T}} \, \right]
 x, y)




LaTeX Math Block
anchor
T_z
1
alignmentleft
T_D(t,z) = \delta
\Big[ \lambda_e \nabla T_
D
G \
, \exp \left[ \, {(z_s-z}) \sqrt{\frac{\pi}{a_{en} \, D_T}} \, \right] \, \cos \left[ \, 2 \pi \frac{t - \delta t_D}{D_T} + (z_s -z) \sqrt {\frac{\pi}{a_{en} \, D_T}} \, \right]
Big]_{z=z_{ref}} = {\bf j}(x,y, z = z_{ref})



LaTeX Math Block
anchorG_T
alignmentleft
G_T({\bf r}) = \frac{j_z({\bf r})}{\lambda_e({\bf r})
Neutral Layer
LaTeX Math Block
anchorz_N
alignmentleft
z_n = z_s + H_n
LaTeX Math Block
anchorH_N
alignmentleft
H_n = \sqrt{\frac{a_{en} \, A_T }{\pi}} \, \ln \frac{\delta T_A }{\delta T_{\rm cut}
}



See Also

...

Geology / Geothermal Temperature Field

Constant Areal Geothermal Temperature Profile @model ] [ Geothermal Temperature Gradient ]

...